1. Field of the Invention
The present invention relates to body fat measurement devices configured to be capable of calculating a body fat mass of a measurement subject by measuring a body impedance, and particularly relates to body fat measurement devices configured to be capable of measuring a body fat mass such as a visceral fat mass with ease.
2. Description of the Related Art
In recent years, body fat mass is gaining attention as an indicator used to determine the health of a measurement subject. In particular, visceral fat mass is gaining attention as an indicator for determining whether or not a person is suffering from central obesity. Central obesity is said to bring about lifestyle-related diseases that can easily lead to artery hardening, such as diabetes, hypertension, and hyperlipidemia, and the stated indicators hold promise in terms of preventing such diseases. “Visceral fat” refers to fat that accumulates around the internal organs on the inner side of the abdominal muscles and the back muscles, and is distinct from the subcutaneous fat that is located toward the surface of the trunk area. It is typical to employ the area occupied by visceral fat in a cross-section of the trunk area that corresponds to the navel (referred to as a “visceral fat cross-sectional area” hereinafter) as an indicator of the visceral fat mass.
Normally, visceral fat mass is measured by analyzing images obtained through X-ray computed tomography (CT), magnetic resonance imaging (MRI), or the like. In such image analysis, the visceral fat cross-sectional area is calculated geometrically from a tomographic image of the trunk area obtained by using X-ray CT, MRI, or the like. However, it is necessary to use several pieces of large equipment installed in a medical facility, such as X-ray CT, MRI, or other machines, in order to make use of such a measurement method; thus it is extremely difficult to measure visceral fat mass on a daily basis through such a measurement method. X-ray CT also poses the problem of exposure to radiation, and thus cannot necessarily be called a desirable measurement method.
A body impedance technique is being considered as an alternative to these measurement methods. The body impedance technique is a method for measuring body fat mass widely used in household-based body fat measurement devices; in this technique, electrodes are placed in contact with the four limbs, the body impedance is measured using those electrodes, and the body fat mass is calculated from the measured body impedance. The stated household body fat measurement device makes it possible to accurately measure the extent of body fat buildup throughout the entire body or in specific areas such as the four limbs, the trunk area, or the like.
However, conventional body fat measurement devices that use the body impedance technique measure the extent of body fat buildup throughout the entire body or in specific areas such as the four limbs, the trunk area, or the like, as mentioned earlier, and are not capable of accurately extracting and measuring the extent of visceral fat buildup, the extent of subcutaneous fat buildup, and the like individually. This is because, as mentioned above, conventional body fat measurement devices are configured so that the electrodes are attached only to the four limbs, and thus the visceral fat and subcutaneous fat cannot be accurately measured individually.
Accordingly, bringing electrodes into direct contact with the trunk area, measuring the body impedance using those electrodes, and individually and accurately calculating the visceral fat mass and the subcutaneous fat mass based on that measurement is being considered as a way to solve this problem.
For example, JP 2002-369806A discloses a body fat measurement device configured so that electrodes are provided on the inner circumferential surface of a belt member and the belt member is wrapped around and anchored to the trunk area of a measurement subject, thus placing the electrodes in contact with the trunk area.
Meanwhile, JP 2005-288023A, JP 2008-23232A, and so on disclose body fat measurement devices configured so that electrodes are provided on the surface of a fitting unit that is fitted to the abdominal area of a measurement subject and the fitting unit is pressed against the abdominal area, thus placing the electrodes in contact with the abdominal area.
Furthermore, JP 2008-295881A discloses a body fat measurement device configured so that electrodes are provided on the inner circumferential surface of a belt member and the belt member is wrapped around and affixed to a measurement subject's trunk area, and electrodes are provided on clip-shaped members and the clip-shaped members are affixed to the measurement subject's arms and legs, thus placing electrodes in contact with the abdominal area and arms and legs of the measurement subject, who is lying face-up.
In addition, although not discussing a specific device configuration, JP 2008-228890A mentions being able to accurately measure visceral fat mass and subcutaneous fat mass by placing electrodes in contact with the back of a measurement subject's trunk area (that is, the back) without placing electrodes in contact with the measurement subject's abdominal area and placing electrodes in contact with the arms and legs of the measurement subject, measuring the body impedance, and calculating the visceral fat mass and the subcutaneous fat mass based on the measured body impedance. One of the reasons for this is that the subcutaneous fat that accumulates on the abdominal area side is relatively thinner than the subcutaneous fat that accumulates on the back area side, and thus if the electrodes are placed in contact with the abdominal area, the current that is applied will flow through fat-free areas, which makes it easy for errors to occur.
Meanwhile, to make it possible to measure the visceral fat mass, subcutaneous fat mass, and so on with a high degree of accuracy using the stated body impedance, it is necessary to take actual measurements of the measurement subject's trunk area body build, such as the circumferential length of the trunk area, the trunk area width, and the trunk area depth, and use the measurements in computation processes for calculating the body fat mass.
For example, according to the body fat measurement device disclosed in the stated JP 2005-288023A, a fitting unit that is fitted to a measurement subject's abdominal area is provided upon a pair of arm portions, which make contact with both sides of the measurement subject's trunk area (in other words, both flanks), so that the fitting unit is mobile; the trunk area width is measured by bringing the arm portions into contact with both flanks, and the result of that actual measurement is used in computation processes for calculating body fat mass.
In addition, according to the body fat measurement device disclosed in the stated JP 2008-23232A, a fitting unit that is fitted to a measurement subject's abdominal area is provided upon an arm portion, which makes contact with the measurement subject's back, so that the fitting unit is mobile; the trunk area depth is measured by bringing the arm portion into contact with the back, and the result of that actual measurement is used in computation processes for calculating body fat mass.
Furthermore, in the body fat measurement device disclosed in the aforementioned JP 2008-295881A, an actual measurement of the circumferential length of the trunk area is taken by detecting the length at which the belt member worn on the trunk area of the measurement subject is wrapped, and the result of that actual measurement is used in computation processes for calculating a body fat mass.
As described above, it is necessary to bring electrodes into contact with a measurement subject's trunk area and take an actual measurement of the measurement subject's body build at the trunk area, as represented by the circumferential length of the trunk area, the trunk area width, the trunk area depth, and so on, in order to measure a visceral fat mass and the like with a high level of accuracy through the body impedance technique. To measure the visceral fat mass and the like more accurately at this time, it is essential to position the electrodes that are to be placed in contact with the measurement subject's trunk area precisely on the trunk area, and to position a distance measurement means for actually measuring the measurement subject's body build precisely around the trunk area.
In the case where, for example, the electrodes have not been correctly positioned relative to the measurement subject's trunk area, the measured body impedance will contain a high degree of error, resulting in a high degree of error in the calculated visceral fat mass or the like. Furthermore, in the case where, for example, the distance measurement means has not been correctly positioned relative to the measurement subject's trunk area, the measured body build information of the measurement subject's trunk area will contain a high degree of error, resulting in a high degree of error in the calculated visceral fat mass or the like. Accordingly, the body fat measurement device is normally configured so that the electrodes, distance measurement means, and so on are positioned using the measurement subject's navel as a reference, and the body fat measurement device employs a configuration in which various types of indicators and the like used for this positioning are provided.
Here, in the case where the electrodes to be placed in contact with the trunk area and the distance measurement means are to be integrated into a single unit, as disclosed in the aforementioned JP 2005-288023A, JP 2008-23232A, and JP 2008-295881A, both the electrodes and the distance measurement means are to be precisely positioned relative to the trunk area through a single positioning operation.
However, with the body fat measurement devices disclosed in the aforementioned JP 2005-288023A and JP 2008-23232A, in the case where actual measurements of the trunk area width and the trunk area depth are to be taken by bringing the arm portions provided in a mobile state into contact with the trunk area, the measurement subject or the like is forced to carry out operations for individually moving the arm portions along two directions of the trunk area, or the forward/backward direction and the right/left direction; thus there is a problem in that the body fat measurement device is not necessarily easy to use. These operations become extremely complicated particularly in the case where the body fat measurement device is configured so that the measurement subject him/herself can perform the measurement alone, without the help of an assistant or the like; this greatly inhibits taking measurements of a visceral fat mass or the like in a simple and easy manner.
Meanwhile, in the case where the configuration is such that an actual measurement is taken of the circumferential length of the trunk area using a belt member in which electrodes are provided, as with the body fat measurement device disclosed in the aforementioned JP 2008-295881A, the measurement subject or the like is forced to perfectly wrap the belt member around his/her trunk area at the proper wrapping strength; thus there is a problem in that the body fat measurement device is not necessarily easy to use. Note that it is preferable to employ the trunk area width and trunk area depth, using which the cross-sectional area of the measurement subject's trunk area can be estimated more accurately, as the body build information that should be measured for the measurement subject; from this point of view, the body fat measurement device disclosed in the aforementioned JP 2008-295881A has room for improvement.
In this manner, conventional body fat measurement devices have not necessarily been easy to use, and have been problematic in that accurate body fat measurement could not be carried out in an easily-repeatable manner.